Technical Field
The present disclosure relates to a technology for diagnosing the deterioration of a selective catalytic reduction (SCR) catalyst arranged in an exhaust passage of an internal combustion engine.
Description of Background Art
In a first patent literature, there is disclosed a technology in which provision is made for an exhaust gas purification catalyst arranged in an exhaust passage of an internal combustion engine, an air fuel ratio sensor arranged in the exhaust passage at a location upstream of the exhaust gas purification catalyst, and an air fuel ratio sensor arranged in the exhaust passage at a location downstream of the exhaust gas purification catalyst, wherein when the exhaust gas purification catalyst is in a low temperature state in which it begins to be activated, the deterioration of the exhaust gas purification catalyst is diagnosed based on a difference in the outputs of two air fuel ratio sensors (hereinafter referred to as a “sensor output difference”). In addition, in the first patent literature, it is suggested that a diagnosis according to the method described above can be applied, in cases where an SCR catalyst is used as the exhaust gas purification catalyst, too.